The field of the invention is antennas. The invention is directed to a compact multiband antenna for portable devices.
Portable devices that communicate with wireless services frequently must operate in different frequency bands. Different frequency bands may be used, for example, in different geographical regions, for different wireless providers, and for different wireless services. Pagers, data terminals, mobile phones, other wireless devices and combined function wireless devices therefore often require an antenna or multiple antennas responsive to multiple frequency bands. As an example of the need for multi-band reception and transmission, high end xe2x80x9cworldxe2x80x9d mobile phones need to accommodate at least three bands to account for two European (GSM/DCS) and one United States (PCS) band. A fourth band might even be required to account for additional services. A single antenna is desirable for obvious reasons of size and appearance, critical issues in wireless devices.
Although there are several designs available for external multi-band antennas, the trend in portable communication devices is to house the antennas internally or within or on the external device housing. Existing production internal antennas are either single- or dual-band designs.
A multibanded PIFA (planar inverted-F) antenna of the invention provides multiple operating bands in a suitable compact configuration for portable communication devices. A preferred embodiment makes use of a spiral slot. The spiral slot is formed to cause multiple frequency dependent nulls in the antenna""s electric field modal distribution. The preferred embodiment antenna has a single element patch radiator formed on a dielectric support in an inverted-F relationship with a first ground plane. The dielectric support may be part of a device housing or internal board, e.g., a PCB board. The patch radiator includes a spiral slot. A feed is made to the patch radiator in a location relative to the spiral slot to ensure that portions of the single element patch radiator enclosed by the spiral slot are fed as a series extension of another portion of said patch radiator. According to a preferred embodiment, the patch radiator may be formed from a single conductive sheet, plating or deposit along with the shorting post and feed. A majority of its surface area is formed in a primary plane and its remaining surfaces define, generally perpendicular from the primary plane, a feed extending from a first edge of the primary plane and a shorting post extending from a second edge of the primary plane. A tab may be formed to add radiator surface area and may extend, for example, perpendicular from a third edge of the primary plane.
A single spiral slot will cause the antenna to have two primary resonances. Adding an additional spiral will double the number of resonances. An alternate way of increasing the number of resonant modes is to add a second ground plane electrically opposing only a portion of the single element patch radiator including the feed. The shorting post is from the antenna to the first ground plane and the first and second ground planes are connected together at some point. The effect of additional ground plane is to double the number of resonant modes of the antenna. These modes can be tuned by adjusting the location of the feed and spiral slot. The second ground plane can also be used to create additional bands in the absence of the spiral slot.